You can't technology your way out of social problems. The conflicting requirements raised throughout the article are, indeed, ultimately unsolvable.
The only way to stop an oppressive government from abusing the emergency notification system for propaganda is to fight against the oppressive government until it stops existing, then keep fighting to prevent it from existing again.
The only way to stop an oppressive government from abusing the emergency notification system for propaganda is to fight against the oppressive government until it stops existing, then keep fighting to prevent it from existing again.